Your mother said: You have to g re et your uncle!
Greeting (with 'u') is the same as salutation, it comes from the verb 'to fulfill', because whoever fulfilled something, executed the greeting.
'to give fulfillment' to something is the same as 'to perform'. Ex.: The promised work was fulfilled.
'by fulfillment' is rarely used, but it is still used when someone does something unwillingly, merely out of formal, etiquette requirement. (source Priberam Dictionary).
On the other hand, the word Length (with 'o') refers to a measure. The distance between two points.
To not forget:
Remember that "taking it in the CU'mprimento" - may not be a very usual greeting, but the suggestion is valid.
