overthin
1 of 2adjective
over·thin ˌō-vər-ˈthin 
: excessively thin
overthin paint
She was … overthin, as if a hypercharged metabolism was burning off calories faster than she could stuff them into her mouth.
Bonnie MacDougal
Bonnie MacDougaloverthin
2 of 2verb
overthinned; overthinning
transitive + intransitive
: to make (something) too thin : to thin (something) too much
overthinning a tree with too much pruning
It is thinned with water just as the paints are, but care should be taken not to overthin and lose the quality of the gesso. William F. Powell
William F. Powell
Word History
First Known Use
Adjective
circa 1639, in the meaning defined above
Verb
1819, in the meaning defined above