Equivalent to light brown horse I'm obliged to break in (10)
I believe the answer is:
tantamount
'equivalent' is the definition.
(I know that equivalent can be written as tantamount)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tantamount that I've seen before include "Virtually equivalent (to)" , "Equivalent in seriousness (to)" , "Equivalent in value (to)" , "Equal in value" .)