1) Asked 2) Bound 3) Compelled 4) Compulsory 5) Entailed 6) Essential 7) Legit 8) Mandatory 9) Necessary 10) Need be 11) Needed 12) Needful 13) Obligatory 14) Requisite 15) Took 16) Wanted 1) Compulsory 2) Enforced 3) Essential 4) Essential, compulsory 5) Hunted 6) Like some courses 7) Necessary 8) Needed 9) Needful 10) Obligatory 11) Required by rule 12) Requisite 13) Sought 14) Sought after 15) Unavoidable 
• (imp. & p. p.) of Require
required 1. Necessary or appropriate. 2. Insisted upon or imposed as a condition.
[ASVAB glossary] necessary by rule[Academic words] necessary by rule