From The Collaborative International Dictionary of English v.0.48 [gcide]:
Overshadow \O`ver*shad"ow\, v. t. [imp. & p. p. Overshadowed;
p. pr. & vb. n. Overshadowing. ] [Cf. Overshade. ]
1. To throw a shadow, or shade, over; to darken; to obscure.
[1913 Webster]
There was a cloud that overshadowed them. --Mark ix.
7.
[1913 Webster]
2. Fig.: To cover with a superior influence; to be viewed as
more important than. --Milton.
[1913 Webster +PJC]
3. To cause to be sad or disappointing; to cast a sad shadow
on; as, an accidental death overshadowed the joy of the
festival.
[PJC]
From WordNet (r) 3.0 (2006) [wn]:
overshadow
v 1: be greater in significance than; "the tragedy overshadowed
the couple's happiness" [syn: overshadow, dominate,
eclipse]
2: make appear small by comparison; "This year's debt dwarfs
that of last year" [syn: shadow, overshadow, dwarf]
3: cast a shadow upon; "The tall tree overshadowed the house"