Understanding company with mass potential (10)
I believe the answer is:
compromise
'understanding' is the definition.
(I know that compromise is a type of accommodation)
'company with mass potential' is the wordplay.
'company' becomes 'co' (abbreviation).
'with' means one lot of letters go next to another.
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'potential' becomes 'promise' (I've seen this in another clue).
'co'+'m'+'promise'='COMPROMISE'
(Other definitions for compromise that I've seen before include "Settlement" , "Give-and-take" , "Agree a middle way" , "accommodation" , "Middle course" .)