Hard to move in embrace that's unpleasant (3)
I believe the answer is:
ugh
'that's unpleasant' is the definition.
(expression of disgust)
'hard to move in embrace' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to' means one lot of letters go next to another (I've seen this in other clues).
'move in embrace' becomes 'ug' (I can't justify this - if you can you should give a lot more credence to this answer).
'h' put after 'ug' is 'UGH'.
Can you help me to learn more?
(Other definitions for ugh that I've seen before include "Exclamation of disgust arising from hug" , "Exclamation of horror" , "Kind of hug - it's disgusting" , "Disgust in thought" , "That's disgusting!" .)