What's the difference between underlying and undersong?

Underlying

Definition:

(a.) Lying under or beneath; hence, fundamental; as, the underlying strata of a locality; underlying principles.

Example Sentences:

(1) The resulting dose distribution is displayed using traditional 2-dimensional displays or as an isodose surface composited with underlying anatomy and the target volume.
(2) Because of the short detachment interval, and the absence of underlying pathology or trauma, the recovery process described here probably represents an example of optimum recovery after retinal reattachment.
(3) Steroids are not recommended because they may compromise defenses against an underlying disease process.
(4) The results obtained further knowledge of the anatomy of the nuclei, specifically the areas used for the prosthesis implantation and the underlying tissue.
(5) The final model has a probability 0.08 of underlying survival time being zero and, given non-zero survival time, takes the form of an exponential distribution with mean of 14.95 months.
(6) Certain underlying factors in several types of retinal degeneration are first discussed, followed by characteristics of diabetic maculopathy and of other types of macular degeneration including that due to aging.
(7) Contributing factors could include advanced age and underlying clinical or subclinical brain disease.
(8) In all cases, the evaluation depends on the continuous observance of the patients, taking into account any underlying primary illness (alcoholism, cerebral vascular disease, conditions following brain surgery or trauma).
(9) Recent rapid developments in molecular biology have started to clarify the underlying pathophysiology of various neurological diseases.
(10) The aim of this study was clarify the physiopathological mechanisms underlying atrial pauses as well as to evaluate the sensitivity of sinoatrial conduction time (SACT) directly measured on SNE and of SACT estimated with the indirect Strauss method with respect to the detection of SSS.
(11) The second has various underlying diseases, such as chronic hypertension or renal disease, etc..
(12) Skeletal muscle mtDNA of three patients with mitochondrial encephalomyopathy, characterized clinically by myoclonic epilepsy and ragged-red fiber (MERRF) syndrome, has been sequenced to determine the underlying molecular defect(s).
(13) Alveoli underlying the plasma membrane sometimes contain binding sites, particularly on their outer membranes.
(14) Predictions were comparatively poor for the underlying disorder category (10%).
(15) Both IGF-I and growth hormone have the potential to improve muscle mass and function in patients who are catabolic due to the severity of their underlying disease state.
(16) The mechanisms underlying the three types of Cd effects on the frog skin were discussed in relation to the Na, K-ATPase activity.
(17) The median age of patients with bacteremia of unknown origin was 65 years, and their most common underlying disorders were solid malignancy (28% of patients) and diabetes mellitus (18%).
(18) We postulate that an abnormality in retinal dopaminergic neurons, which are known to reduce light responsiveness of horizontal and ganglion cells, is the underlying pathophysiology of this clinical finding.
(19) The development of renal insufficiency during enalapril therapy may be exacerbated by concomitant diuretic therapy and should raise the suspicion of underlying transplant renal-artery stenosis.
(20) In each case the finding of anti-neutrophil cytoplasm antibodies (ANCA) strongly suggested an underlying vasculitic pathology, Wegener's granulomatosis.