From WordNet (r) 2.0 (August 2003) [wn]:
flavorless
adj : lacking taste or flavor or tang; "a bland diet"; "insipid
hospital food"; "flavorless supermarket tomatoes";
"vapid beer"; "vapid tea" [syn: bland, flat,
flavourless, insipid, savorless, savourless,
vapid]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
flavorless \fla"vor*less\, a.
Without flavor; tasteless. Opposite of flavorful.
Syn: bland, flat, flavourless, insipid, savorless.
[1913 Webster + WordNet 1.5]