Definition: a letter or letters added to a word before or after it, only to signify some specific purpose such as (a) the addition of an afix (e. g. क्त्रि, अथुच् अङ् etc.) or (b) the substitution of गुण, वृद्धि or संप्रसारण vowel or (c) sometimes their prevention. These anubandha letters are termed इत् (lit. going or disappearing) by Pāṇini (cf. उपदेशेजनुनासिक इत् etc. I.3.2 to 9), and they do not form an essential part of the word to which they are attached, the word in usage being always found without the इत् letter. For technical purposes in grammar, however, such as आदित्व or अन्तत्व of affixes which are characterized by इत् letters, they are looked upon as essential factors, cf. अनेकान्ता अनुबन्धाः, एकान्ता:, etc, Par. Śek. Pari. 4 to 8. Although पाणिनि has invariably used the term इत् for अनुबन्ध letters in his Sūtras, Patañjali and other reputed writers on Pāṇini's grammar right on upto Nāgeśa of the 18th century have used the term अनुबन्ध of ancient grammarians in their writings in the place of इत्. The term अनुबन्ध was chosen for mute significatory letters by ancient grammarians probably on account of the analogy of the अनुबन्ध्य पशु, tied down at sacrifices to the post and subsequently slaughtered.