BT Pes 40b(2) :ההיא ארבא דטבעא באשתא‏ : a certain boat that sank on its bottom
See the entire entry for ˀeššaṯ, ˀeštā n.f. foundation, base

BT Pes 40b(2) :ההיא ארבא דטבעא באשתא‏ : a certain boat which sank (in the canal) up to its hold
See the entire entry for ṭbˁ vb. to seal; to sink