The Collaborative International Dictionary of English v.0.48:

magnetic disc \magnetic disc\, magnetic disk \magnetic disk\n.
   A ditical memory device consisting of a flat disk covered
   with a magnetic coating on which information is stored; a
   hard disk, floppy disk, and diskette are typically
   magnetic disks.

   Syn: disk, disc.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

diskette \diskette\ n. (Computers)
   a data-storage medium consisting of a small plastic disk
   coated with a thin layer of magnetizable material on one or
   both sides, enclosed in a stiff envelope with a radial slit.
   It is used in a specially designed disk drive, in which the
   disk is rotated at high speed, and which stores data on the
   disk by causing changes in the direction of magnetization of
   the magnetic layer as the disk spins and as sequential
   locations on the disk pass under the read-write head of the
   drive. Reading of the data occurs in the reverse process, by
   detection of the patterns of magnetization of the disk. Such
   disks are used to store data or programs for a microcomputer.

   Syn: floppy, floppy disk.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

diskette
    n 1: a small plastic magnetic disk enclosed in a stiff envelope
         with a radial slit; used to store data or programs for a
         microcomputer; "floppy disks are noted for their relatively
         slow speed and small capacity and low price" [syn:
         diskette, floppy, floppy disk]

The Free On-line Dictionary of Computing (30 December 2018):

floppy disk
crunchy
diskette
double density
floppy
HD
high density

    (Or "floppy", "diskette") A small,
   portable plastic disk coated in a magnetisable substance used
   for storing computer data, readable by a computer with a
   floppy disk drive.  The physical size of disks has shrunk from
   the early 8 inch, to 5 1/4 inch ("minifloppy") to 3 1/2 inch
   ("microfloppy") while the data capacity has risen.

   These disks are known as "floppy" disks (or diskettes) because
   the disk is flexible and the read/write head is in physical
   contact with the surface of the disk in contrast to "hard
   disks" (or winchesters) which are rigid and rely on a small
   fixed gap between the disk surface and the heads.  Floppies
   may be either single-sided or double-sided.

   3.5 inch floppies are less floppy than the larger disks
   because they come in a stiff plastic "envelope" or case, hence
   the alternative names "stiffy" or "crunchy" sometimes used to
   distinguish them from the floppier kind.

   The following formats are used on IBM PCs and elsewhere:

    Capacity  Density  Width
     360K	   double   5.25"
     720K	   double   3.5"
     1.2M	   high	    5.25"
    1.44M	   high	    3.5"

   Double denisty and high density are usually abbreviated DD and
   HD.  HD 3.5 inch disks have a second hole in the envelope and
   an overlapping "HD" logo.

   (1996-08-23)