I looked again at the Oxford English Dictionary.  It comes into 
English from medieval French 'fix' (modern French 'fixe') partly from 
'fixus' past participle of figo, figere, as you say, but also partly 
via the medieval Latin fixare, which I suspect is one of those Vulgar 
Latin reinterpretations, where the word fixus led them to back-create 
a verb 'fixare', which had no existence in classical Latin.  (You 
know, where, in the late empire, neuter plurals ending in -a were 
reinterpreted as feminine singulars ending in -a and conjugated 
accordingly, that sort of thing.)

Martin

>Thanks Martin,
>
>I can't find 'fixare' in my (very small!) latin dictionary, but it 
>has 'fixi' as the perf. tense of 'figo', which includes 'to drive 
>in,  pierce' as part of it's meaning, not unlike the meaning of 
>'defigo',  the root of 'defixiones' , and pertaining to the nailing 
>or attaching  of the curse - there is a group of early modern 
>english 'defixiones',  which are very like the ancient ones in 
>content - perhaps the word  came back into use at that time along 
>with the practice?
>
>Faith Morgan
>
>On 30 Nov 2005, at 22:26, [log in to unmask] wrote:
>
>>>hello
>>>
>>>does anyone know whether the phrase 'to fix a race' might come 
>>>from 'defixiones' which were often
>>>used to try to 'fix' a race...?
>>
>>Sorry, but 'fix' only come into English in the 16th century, 
>>according to the OED.  It's from Latin 'fixare', but a bit mundane, 
>>I'm afraid.
>>
>>Martin Nichols