There are some words that I think belong in our common words, because most people would probably have encountered them, even though they are far from everyday words. But is
oviduct such a word? I think
ovine, which was in the same puzzle, belongs in that category. But
ovine was played by 104 people, while
oviduct was found by only 15, although this might be partly due to the fact that
ovine comes up in our puzzles more often, so some players might know it only from Chi.
But
oviduct seems to be used quite infrequently in print, and then often in specialist titles, like
Smallholder and
Horsetalk. I don't know of any way to assess the frequency of use of words in TV nature documentaries, though
an article in the Atlantic mentions that episode 6 of David Attenborough's classic
Life on Earth series covered "a
Nectophrynoides toad, which raises her tadpole inside her body on flakes of oviduct tissue, and gives birth to the froglet by squeezing it out
with her lungs."
On the whole I feel that
oviduct falls a little below the threshold of visibility. It will be treated as a rare word in future.