we've talked about the Welsh w (cf. cwm), haven't we?

Forms: 1–4 sweord, (1 sueord, swurd), 1, 4 (6 Sc.) suord, 1, 6 swyrd, 3–5 (6 Sc.) suerd, 3–6 swerd, (3 swærd, swuerd), 4–6 swerde, sworde, (4 surd, squorde, Ayenb. zuord, 4–5 swerid, swert, 5 sward, swirde, swhirde, squrd, sqwerd, 6 sweard(e, swyrde, swurde, shorde, showrde, swourd, swoord(e, Sc. swrd, sourd), 1, 5– sword. [OE. sweord str. n. = OS., OFris. swerd, MLG. swert, MDu. swaert (Du. zwaard), OHG., MHG. swert (G. schwert), ON. sverð (Sw. svärd, Da. sverd)

the first known written usage is from Beowolf:
Helmas and heard sweord.