A puppy looking out of a window.
An example of something that would be described as plaintive would be the sad whimper of a puppy whose owners have just left him all alone.
Origin of plaintiveMiddle English pleintif ; from Old French plaintif: see plaintiff
Origin of plaintiveMiddle English plaintif, from Old French, aggrieved, lamenting, from plaint, complaint; see plaint.
(comparative more plaintive, superlative most plaintive)
From Old French plaintif (“aggrieved, lamenting"), from plainte (“lament, complaint"); see plaint.