Definition of a contractible simplicial complex without appealing to topological realization

Let $\Delta$ be a simplicial complex. I believe the standard definition of $\Delta$ being contarctible is if the topological realization $|\Delta|$ is contractible. However, I am seeking a definition of a contractible simplicial complex that is in terms of the simplicial complex qua simplicial complex, possibly having something to do with its simplicial homology. In other words, something in terms of the faces or its simplicial homology or something that can be checked while staying in the category of simplicial complexes. Call such a definition $S$-contractible. I would then hope that a simplicial complex is $S$-contractible if and only if $|\Delta|$ is contractible. Is anyone aware of such a definition and if so, has it been shown to agree with the standard definition of contractible? Many thanks in advance.

-
If you use the more flexible language of simplicial sets, then there is a purely combinatorial notion of homotopy which can be used to express contractibility (and then a (Kan) simplicial set is contractible if and only if its geometric realization is). –  Akhil Mathew Jun 10 '12 at 23:06
Thanks for the replies. I'll look carefully at the simplicial approximation theorem to see if I can make it work. I guess what I had in mind comes from the analogy with a 1-dimesional complex. If we view a 1-dimensional simplicial complex as a graph $G$, then $|G|$ is contractible if and only if $G$ is a tree. There are lots of good and easy to understand definitions of a tree. Something like a higher dimensional analogue of a tree is what I was hoping for. –  Sora Jun 9 '12 at 1:51