Sinking Copy link Sinking , adjective and noun a. & n. from Sink. Collocations (3) Sinking fund , See under Fund. Sinking head (Founding) , a riser from which the mold is fed as the casting shrinks. See Riser, n., 4. Sinking pump , a pump which can be lowered in a well or a mine shaft as the level of the water sinks.