【Apparent】 , 【illusory】 , 【seeming】  and ostensible all mean not really or actually being what it appears to be.

Something is 【apparent】 that, however evident it may be from the point of view of the unaided senses, is not borne out by scientific investigation or by a knowledge of all the facts or circumstances.

• the 【apparent】 size of the sun
• the 【apparent】 loss of weight of a body immersed in water
  —Darrow
• I am anxious to leaven our 【apparent】 , for it is really more 【apparent】 than real, our 【apparent】 worldliness
  —Mackenzie}

Something is 【illusory】 that is the result of a false impression and acquires a character or appearance other than that found in the real thing or that seems to exist when it is actually nonexistent.

The deception may be the result of one’s sense limitations (as in an optical illusion), of a misleading appearance assumed by certain natural phenomena (as a mirage or will o’ the wisp), of one’s own state of mind which colors or alters the objective reality, or of the strong stimulation of the imagination (as by a work of art) that causes one to accept as real something purely imaginary.

• lengthwise stripes give an 【illusory】 height to the figure
• 【illusory】 pools of water on a highway
• a lover often attributes an 【illusory】 beauty to his beloved
• the beautiful is in a certain sense 【illusory】 , or rather contains an element of illusion
  —Alexander

Something is 【seeming】 that is so like the reality in appearance that it may be mistaken for it. 【Seeming】 usually implies a character in the thing observed rather than, as with the two preceding words, a defect of observation. Often it suggests an intent to deceive or delude.

• Miss Wilmot’s reception [of him] was mixed with 【seeming】  neglect, and yet I could perceive she acted a studied part
  —Goldsmith
• the whole of Burns’s song has an air of straight dealing . . . but these 【seeming】 simplicities are craftily charged . . . with secondary purposes, ulterior intimations
  —Montague

Something (as an aim or motive) is ostensible that is explicitly declared, professed, or avowed or that has the outward marks of the character ascribed to it yet has in fact another hidden aim, motive, or character; thus, to say that the ostensible purpose of a naval review is the celebration of a national holiday may imply the presence of another, deeper, and more significant purpose not revealed (as mobilization for war).

• natives from independent and feudatory courts whose ostensible business was the repair of broken necklaces . . . but whose real end seemed to be to raise money for angry Maharanees or young Rajahs
  —Kipling)