Zentai derives from 全身タイツ. The first kanji is 全 and means as a noun entire, complete, overall. As prefix zen it means all, pan… The second Kanji is 身. As noun it means body, main part, or oneself…. together is reads as  ‘full body’ or ‘the whole body’. But read at a hiragana level it also translate to “past life”… (P-J Van Haecke)