Praise highly, though out of key (5)
I believe the answer is:
exalt
'praise highly' is the definition.
(I've seen this in another clue)
'out of key' is the wordplay.
'out of' becomes 'ex' ('out of' in Latin).
'key' becomes 'alt' (the Alt keyboard button).
'ex'+'alt'='EXALT'
'though' acts as a link.
(Other definitions for exalt that I've seen before include "Praise - latex (anag)" , "(P) raise" , "Extol" , "Raise in praise" , "Praise, glorify, or honour" .)