(modal) Seemingly, apparently, on the surface; supposedly, according to representations or implications made by someone (especially when their motives are suspected by others).
Near-synonyms: reportedly, reputedly, purportedly, putatively, rumoredly, supposedly, allegedly, possibly, probably, likely, plausibly, presumably; see also Thesaurus:ostensibly
His interest in the railway was ostensibly a hobby, but people began wondering why he was taking photos of specific trains and specific equipment.
Her interest in his welfare was ostensibly charitable and magnanimous, but people began wondering who was going to inherit his assets when he died.