Tammy is a diminutive of Tamar — from the Hebrew Tamar ("palm tree"). A top-15 US baby name from 1965 to 1971, peaking at #11 in 1967 — popularized by the 1957 film Tammy and the Bachelor starring Debbie Reynolds. Tammy Duckworth (born 1968) — Thai-American US Senator from Illinois; first Asian-American senator from Illinois, first US Senator born in Thailand, first woman with a disability elected to Congress (lost both legs as a Black Hawk helicopter pilot in Iraq, 2004). Tammy Faye Bakker (1942-2007) — American televangelist and pop-culture icon. Tammy Baldwin (born 1962) — first openly lesbian US Senator (Wisconsin, 2013).
Subject of Michael Showalter's The Eyes of Tammy Faye (2021 film) starring Jessica Chastain.
In Pythagorean numerology the letters of Tammy reduce to 9, The Giver. This is a traditional interpretive system, not a factual claim about the name.