<fenten> ‘spring, well’ + <Madern> Personal name – Madron {<matis - mas> ‘good’ + <ternus> ???} (Gover, The Place-Names of Cornwall, 1948, p. 719)
Historic forms:
Maderne Well 1584 Weatherhill
Maderne Well c.1590 Weatherhill
S. Madderns Well 1654 Weatherhill
Madren Well 1668 Weatherhill
Madron Well 1745 Weatherhill
Madron Well 1974 (OS 1974)
Madron Well 1995 (OS 1995)