underfeed

verb (used with object), un·der·fed, un·der·feed·ing.

1. to feed insufficiently.
2. to feed with fuel from beneath.

verb (ˌʌndəˈfiːd) -feeds, -feeding or -fed (tr)

1. to give too little food to
2. to supply (a furnace, engine, etc) with fuel from beneath

noun (ˈʌndəˌfiːd)

3. an apparatus by which fuel, etc, is supplied from below