Sentence:  I caught the train just after you went (it was a good idea, that pillion ride - though pretty awful <WSD>pillioning</WSD> with a suitcase and masterpiece in one's arms!) and dumped the m-p in London on Emery Walker, to be photographed half size and collotyped, 100 copies. 
Meaning of the word marked with <WSD> tags:  To ride on a pillion.