The most common and most likely answer to this crossword clue is the 8 letter word STEEPISH
I've seen this crossword clue in The Times
S
T
E
E
P
I
S
H
More clues leading to the result STEEPISH
- Rather stiff after exercising, sip these
- After energy-packed move, one's husband's pretty demanding
- Embarrassed with Thai starter, not hot but quite exorbitant
- Sheep sit on the rocks, quite high
- Quite inclined to bathe with one’s husband
- To soak is hard, and a bit expensive
- Quite difficult to sort out the spies
Buddy explains!

The straight part
We know that "Rather stiff" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rather stiff = steepish.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.