tamp /tæmp/ BrE AmE ( also tamp down ) verb [transitive always + adverb/preposition]
[ Date: 1800-1900 ; Origin: Perhaps from tampion , tampin 'plug, cover' (15-20 centuries) , from French tampon ; ⇨ ↑ tampon ]
to press or push something down by lightly hitting it several times:
The old man tamped down the tobacco with his thumb.