Do words that have been explained in one part of the act have to neccesary be assigned the same meaning in another act ?
The principle of special laws overriding general laws is applicable to the Indian Penal Code.
For references where this has been applied, see paragraph 14;
Ajoy Kumar Banerjee & Ors. Etc vs Union Of India & Ors. Etc
(i) The Legislature has the undoubted right to alter a law already promulgated through subsequent legislation, (ii) A special law may be altered, abrogated or repealed by a later general law by an express provision,
(iii) A later general law will override a prior special law if the two are so repugnant to each other that they cannot co-exist even though no express provision in that behalf is found in the general law, and (iv) It is only in the absence of a provision to the contrary and of a clear inconsistency that a special law will remain wholly unaffected by a later general law. Maxwell-"Interpretation of Statutes Twelfth Edition pp. 196-198, referred to.