J. Payne Smith (ed.), A Compendious Syriac Dictionary Founded upon the Thesaurus Syriacus of R. Payne Smith (Oxford: Clarendon 1903) is available online through Tyndale Archive of Biblical Studies (Tyndale House).
The Tyndale Archive also includes Gesenius’ 1906 Hebrew and Aramaic dictionary, Wilson’s 1850 Hebrew dictionary, Lane’s 1860 Arabic lexicon, Crum’s Coptic dictionary, and Jastrow’s rabbinic Hebrew and Aramaic dictionary.
Biblical Studies Online 