Time-consuming end of Oxford dictionary was far from sound (5)
I believe the answer is:
doted
'was far from sound' is the definition.
(dote once meant to be mentally unsound due to age)
'time-consuming end of oxford dictionary' is the wordplay.
'time' becomes 't'.
'consuming' indicates putting letters inside (consume can mean to bring in or absorb).
'end of' says to take the final letters.
'dictionary' becomes 'oed' (Oxford English Dictionary).
The last letter of 'oxford' is 'd'.
'd'+'oed'='doed'
't' going within 'doed' is 'DOTED'.
(Other definitions for doted that I've seen before include "Was weakly affectionate" , "Was excessively fond" , "- Upon means was foolishly fond of (someone)" , "Lavished affection" , "Showed (excessive) love" .)