1 [mass noun] an aromatic gum or resin which exudes from the bark of a Mediterranean tree, used in making varnish and chewing gum and as a flavouring:incense made from sandalwood, eagle-wood, mastic and cloves
2 (also mastic tree) the bushy evergreen Mediterranean tree which yields mastic and has aromatic leaves and fruit, closely related to the pistachio.
Pistacia lentiscus, family Anacardiaceae
used in names of trees that are similar or related to the mastic tree, e.g. American mastic.
3 [mass noun] a putty-like waterproof filler and sealant used in building:run a bead of mastic along the gap [as modifier]:a mastic sealant [count noun]:use a mastic between the joints
late Middle English: via Old French and Latin from Greek mastikhē (perhaps from mastikhan 'masticate')