The most common and most likely answer to this crossword clue is the 2 letter word HO
I've seen this crossword clue in The Daily Telegraph
H
O
Buddy explains!
The straight part
We know that "Routine" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case routine = ho.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HO mean?
HO noun- A stop; a halt; a moderation of pace.
- Used to attract attention to something sighted, usually by lookouts.
- Halloo; hey; a call to excite attention, or to give notice of approach
- Said as a limb is swung in attack.
- A whore; a sexually promiscuous woman; in general use as a highly offensive name-calling word for a woman with connotations of loose sexuality.
- Care, anxiety, trouble, sorrow.
- To care, be anxious, long.