The word Mangala is an adjective (without the m at the end) meaning auspicious, lucky, propitious, fortunate etc.
The ending referring to 'Mangalam' would mean auspiciousness, propitiousness etc.

The word 'tat' in Sanskrit literally means 'from that' , 'thence'
We cannot confirm that this is the same as Thusness in Buddhism as the contextual nature of the usage has to be taken into account.

Upanishadic comment: 'tatvamasi' thou art that is very famous, meaning, 'thou art the spirit'.
Thusness in Buddhism does not recognise the 'thou' but we would suspsect it focuses on 'immediacy itself' rather than whose immediacy.
The nearest Sanskrit word to thusness we would think is 'asti' in Sanskrit rather than mangalam.

Neither tat nor thusness are really same as mangalam.
Mangalam can also imply being 'lucky' while spirit or thusness surely does not rely on luck

Hinduism has a number of "samskaras", or rites of sacramental purification, which are performed from birth till death. These include:

1) "Garbhadhan samskara", or the purification before a couple conceive a child

2) During pregnancy the child in the womb undergoes two sacraments – "Pumsavana" and "Simanta"

3) At birth, the purificatory ceremony is called "Jatakarma"

4) On the eleventh day after birth the baby is "christened" in a name-giving ceremony called "Namakarana"

5) The child's first feeding of solid food is known as "Annaprasana"

Thus we already have at least 5 purificatory rites in a child's first few weeks of life. The next important ceremony for a boy is variously known in different parts of India as "Mundan", "Chaula" or "Choodakarana". This is the famous hair-cutting ceremony

The baby’s hair from the pregnancy period is not strong. To strengthen the hair roots, the head is tonsured. Removal of hair has both a medical and spiritual benefit. Medically, the scalp is nourished with Vitamin D owing to its exposure to the sun. A tuft of hair left at the back of head, known as a "Shikha" is believed to help protect that part of our brain which helps our memory. Spiritually, this Mundan ceremony is also supposed to spiritualise the body of the child which was only biological until that ceremony - the Shikha is also supposed to denote the place where, for a pious person, the soul leaves the body at the time of death. A similar ceremony is observed with Chinese and Mongolian children as well. Shaving the head is termed as "Ayushkarma" in Sanskrit, the scriptural language of the Hindus. It means enhancing the longevity or the life span of the child. ("Ayuh" in Ayurveda also means this). Shaving the head at the right time is hence important among Hindus. Indeed, traditional Brahmins or priests refer to an almanac each time they go to a barber, while orthodox Hindus do not visit a hair salon on a moonless day! Only renounced monks, known as Swamis or "Sannyasis" shave their head on the Amavasya (moonless) day. Avoiding shaving at night could be based on hygienic concerns.

Mundan as a ceremony is marked for a male child (even though for girls also some communities observe this practice , which is not wrong). The day for the first shave is calculated carefully by referring to the almanac to make sure it is an auspicious moment ( known as a "muhurat" ). It can be done in the 1st year, 3rd year or 5th year of age but it is normally done before the completion of three years of age of the boy. It is all the more important for the traditional Brahmin (priestly) community who are entitled to access to the scriptures through "Upanayan", or spiritual initiation, which commences soon after the Mundan. Without "Upanayan" , a boy cannot become a "dwija", or "twice born" (somewhat synonymous to the Christian terminology of being "born again") ; only after becoming a "dwija" through scriptural studies and general education is one entitled to get married.

Thus Mundan starts a chain of auspicious and responsible roles for an individual in human life according to the Hindu way of life. Other non-Brahmin communities in the Hindu faith also have followed this tradition. But the times have changed enormously from those ancient days when the scriptures were strictly followed. Now girls also cut their hair and even go to the extreme of shaving it!

A young boy’s hair can’t be let grown without cutting for seven or eight years anyway. Hence , the earlier the Mundan is performed, the better. If the child 's whole head cannot be shaven, a partial shaving is usually the solution. If any boy for some reason did not undergo Mundan at a young age, the same has to be observed when he is given "Upanayana" or "Janoi " - the sacred thread -wearing ceremony. A boy, unless he has undergone Mundan, is believed to be not entitled to the benefit for chanting the holy, powerful and rewarding Gayatri Mantra of the mother goddess.

A proper Mundan ceremony involves three rituals of about one hour’s duration – the boy’s parents do a "Ganesh pooja" (worship of the Hindu God Ganesh); a barber who shaves the child receives some honour; and a "Havan" (a purifying ritual with a fire ceremony) with devotional prayers known as the Ayushya Homa mantra and Arati concludes the ceremony. This is followed by a feast and the giving of presents which form the social aspect of the Mundan as a Samskar.

Some of the details in the above mentioned rituals may vary slightly according to the Hindu Smriti or Sutra text (Ashvalayana, Bodhayana, Gautama etc.) which the family might be specifically following in these matters. In North India people usually go to one of the Goddess Durga's temples in the hills and the ceremony is done at the temple of Durga Maa. In the UK people have started doing the ceremony at home with the sacred Havan. 

Dr H V S Shastry
Scriptural & Chaplaincy Executive
Hindu Council UK