विश्वानि शक्रो (R.V.4-16-6). In this Mantra Sayana explains शक्र as शक्रः=समर्थः इन्द्रः, शक्नोति इति शक्रः । In another place परावृक्तं शतक्रतुं (R.V.4-30-16) Sayana explains शतक्रतुः as शतक्रतुः=शतकर्म्मा इन्द्रः । Also Yaska in Nirukta nowhere given such etymology for शक्रः from which we can conclude that शक्रः is an abbreviation.
However, we can not deny such possibility. Because, for some other word Yaska gives such etymology that supports the existence of abbreviation in Vedas. For example, Yaska gives etymology for अग्निः as अक्तात् दग्धात् नीतात् वा, एतेः अकारम् आदत्ते, अनक्तेः दहतेर्वा गकारं, नीपरः, this is an explanation given for अग्निः. Here, taking each letter from each धातु, Yaska shows etymology for अग्निः which is nothing but an abbreviation. Taking clue from this etymology, we can also consider शक्रः as an abbreviation for शतक्रतुः । But one thing which troubles us is that Yaska wherever gives a sort of abbreviational explanation, there he gives by showing the root for that explanation. In शतक्रतुः, the abbreviation we talk about does not have base of root for the same but both शत and क्रतु are सुबन्त ।